Well,... there was just a small error with my manifolds, but now shapeways says: "Based upon the size, volume and wallthickness of your model there is no printer available which is able to print your model. Please adjust the volume and/or size of your model."

Looking at other peoples models is going to be a very misleading venture as the display is scaled to make it fit a percentage of the scene. I scaled your model to 40mm (1.57") across and it uploads fine.

Mmm, well yea. 4cm is a little to big for me.
I'll play with it a little more.

But there is one thing I don't understand; if you have a tip (a spear f.e.), then the tip is getting smaller to the end. At one point it will be smaler then 2mm.
Why does shapeways does not complain at that point?